(From: Wild Bill (email@example.com).)
|NotTaR of small Gasoline Engines and Rotary Lawn Mowers : Engine dies or won't restart when hot
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There can be numerous reasons for the engine to quit running when it
gets up to operating temperature.. expansion of metal parts where
bolts/screws aren't tight enough, breakdown of the condenser for the
ignition points (if equipped), or a possibility of a crack somewhere.
An overall inspection of the tightness of fasteners would be a good place
- If the miss is a miss, the problem probably has to do with ignition or the
fuel mixture. Check the tightness of the carburetor mounting bolts and
where the intake manifold/air-fuel mix tube fastens to the engine block.
- If instead, the miss is popping through the exhaust, this might be caused
by a bad exhaust valve or valve seat.
- If there is puffing or popping near the engine head, the head bolts might
not be tight.
- If the engine spins over too freely when it's hot.. indicating much lower
compression, check the torque of the head bolts.. if they were loose, the
engine should now restart.
- If it won't restart until it's cooled down, the exhaust valve (and/or valve
seat) may be the problem. If you can remove and disassemble the engine
yourself, this isn't expensive to have corrected. If not, the shop labor
for tear-down and reassembly will be fairly costly. A common reason for
exhaust valve failure is that grass clippings become embedded in the cooling
fins around the exhaust port area.
- If the engine is just failing to fire the spark plug when it's hot, there's
a good chance that it's time to change the (points and) condenser. This can
usually be confirmed by quickly removing the spark plug after it quits
running, and grounding the sparkplug base securely to the engine (away from
fuel vapors).. then spin the engine to see if there is a hot blue spark
with an audible snap, snap noise.
(From: Walt Conner (firstname.lastname@example.org).)
As soon as the engine shuts down, turn the flywheel by hand or DISCONNECT
the plug wire and turn the blade by hand to see if there is any
compression. I have had several B&S engines that did not have enough valve
clearance and when hot, the valve stem expands in length enough that the
valve does not properly close. After cooling, engine will be OK. Also could
be a bad condenser or the other faults listed above.
(From: Michael Stevenson (email@example.com).)
Problems with the ignition coil can make an engine impossible to start when
warm (or even stop running when it warms up), apparently this happens on
motorbike engines quite often and is caused by a break in the HT coil.
A carbon track forms inside the coil where the wire is broken. When the
engine is cold the carbon track has a low resistance and it conducts well
enough so the spark is strong enough to start the engine, when the engine is
warmer the track resistance is greater and the spark less strong. This
problem gets worse over time as the carbon track gets bigger and bigger, the
only remedy is to change the coil or electronic ignition module.
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